Control systems for use in plants have been known, in which controllers are connected to respective distributed communication modules to operate the entire control system in coordination with one another via a communication network.
Such a control system is required for exerting real-time performance which enables transmission of communication frames containing a control command and control data via the communication network within a pre-defined period of time.
Meanwhile, so-called cloud computing has been known as one form of the utilization of the computer, in which a server is controlled to carry out actual operations and save data via communication network such as the Internet, providing a user the operations and data for use as a service.
In order to distribute loads to local systems in the control system for a plant, however, introduction of the cloud computing may makes it difficult for the control system to maintain real-time performance.
Meanwhile, conventional local control systems widely adopt sequence control, most of which is implemented as software to operate on a programmable logic controller (PLC).
The PLC as a control device is configured as a compact-size computer and, as with other computers, carries out operations by software on a microprocessor and uses as a behavioral model a state machine which is built upon a relay circuit.
For developing a large-scale control system, control devices (PLCs) need to work in coordination with one another, however, operation allocation to the PLCs is entrusted to designers of the control system. Thus, the operation allocation may not be always optimal.